The invention relates to a method for picking up a plastic product, especially a tacky plastic, and to an apparatus for the practice of the method.
The more or less limp plastic product, depending on its fiber content, viscosity and thickness, has heretofore been handled automatically with needle grippers. The needles usually plunge vertically into the surface of the plastic or at an angle to the surface. In the vertical needle method the plastic adheres to the needles only by friction. Therefore a relatively large number of needles is necessary. In the case of plunging at an angle to the surface, the needles are usually in oppositely slanted pairs. Thus an interlocking clutching of the plastics is achieved. If then these needles are withdrawn in synchronism with one another, the position of the plastic remains centered.
In this needle manipulation of the plastics, marks are formed on the surface of the moldings. The reason is that, when the needles enter the plastic, tacky material has to be displaced. Therefore some plastic adheres to the usually cold needles and has to be removed again for the next plunge because otherwise the plunging force becomes ever greater and ever more material would adhere to the elevated portions. Therefore it is common to clean these needles with stripping sleeves as they are withdrawn. In that case the adhering plastic residues fall onto the surface of the plastic. This surface with the cooled plastic residues is, as a rule, the face side of the plastic. During the pressing operation these cooled plastic residues also remain on the upper side of the plastic, where they are visible as streaks or dots spoiling the surface.
It is furthermore the state of the art that the plastics are extruded or, when they are pressed, usually in the case of the back-pressing of decorative materials, they are processed by the strand-laying method. This method is to be understood to mean that the extruder or injection unit passes across the cavity of the press and deposits the melted, tacky material directly on the cavity. This solves the handling of the material, but the relatively great weight of the extruder also has to be moved and the melting power is reduced by the depositing process.